The present invention relates to electrodes used in taking invasive electrical encephalography (EEG, or electrocorticogram, EcOG) measurement(s). These EEG electrodes are often lumped into two general types, those using surface electrodes and those using depth electrodes.
Epilepsy is a neurological disorder characterized by the occurrence of seizures, specifically episodic impairment or loss of consciousness, abnormal motor phenomena, psychic or sensory disturbances, or the perturbation of the autonomic nervous system. Between 0.5% and 1.0% of the population suffers from epilepsy with approximately 20% having their disease poorly controlled by medications alone. Because epilepsy is characterized by seizures, its sufferers are often limited in the kinds of activities in which they may participate. Depending upon severity of seizures, epilepsy can prevent an individual from driving a vehicle, as well as performing other routine tasks. Some epilepsy sufferers have serious seizures so frequently they may effectively become incapacitated.
Once diagnosed, current treatment modalities for neurological disorders, particularly epilepsy, typically involve drug therapy and/or surgery therapy. While neurologists often turn first to treating epilepsy with drug therapy, the drugs used are not without serious side effects and high costs. Further, for many drugs, it is important to maintain a precise therapeutic serum level to avoid breakthrough seizures (if the dosage is too low) while minimizing toxic effects (dosage gets too high). Surgical approaches are based on the resection of a seizure focus. Implantable electrical stimulation of cranial nerves (especially cranial nerve XII) is also used for the treatment of epilepsy. While direct stimulation of neural tissue in the vicinity of a seizure focus is an emerging therapy for seizure control, the seizure detection capabilities of these systems is currently very limited.
Research on the detection of neurological conditions has focused on receipt and analysis of waveforms referred to in scientific literature as electroencephalogram (EEG) and electrocorticogram (ECoG) waveforms. In general, EEG signals represent aggregate neuronal activity potentials detectable via electrodes applied to a patient's scalp, and EcoG(s) use internal electrodes near the surface of the brain. Thus, ECoG signals, deep-brain counterparts to EEG signals, are detectable via electrodes implanted under scalp and cranium. Unless otherwise specified, “EEG” is used throughout to refer to both EEG and ECoG signals.
This invention is directed to a unique multifunctional Active-Invasive EEG device/system and associated technique comprising one or more surface and/or implantable electrodes—whether depth electrodes, cortical electrodes (subdural), or epidural electrodes. As further explained by applicants in their provisional application No. 60/530,696 (fully incorporated herein by reference) and in the instant disclosure, for simplicity and illustrative purposes, surface-recording electrodes are showcased herein, however within the spirit and scope hereof, depth-, epidural-, subdural-, and so on, type electrodes are contemplated. While the focus hereof is on epileptic disorders, the device/system and technique of the invention is useful for any of a wide variety of neurological disorders experienced by human and non-human/veterinary patients.
The electrode device and associated method of taking EEG measurements according to the invention comprises a plurality of electrode contact-points configured atop a support member. These contact-points are in electrical communication with an integrated circuitry/circuit (“IC” or “chip”) that has converter circuitry adapted for converting analog EEG signals measured—having originated from within a patient—into digital signals. The integrated circuitry is also in electrical communication with a lead assembly that comprises wiring for electrical transmission of the digital signals. The IC is preferably either supported by the support member or this IC is located within the lead assembly slightly ‘downstream’ of the support member, permitting by-and-large “in -situ” processing (e.g., conversion to digital signals) of at least a portion of the analog EEG signals measured from within the patient. The conductive electrode contact-points may contact patient tissue on the surface, epidural, subdural, and so on, for taking the invasive EEG measurements depending upon the specific diagnostic EEG technique employed and associated locale of electrode device.
Neurosurgeons and neurologists may use the instant invention in treating patients with intractable seizures to complement and provide an optimal surgical management. For example, while a patient who suffers from seizures might be treated with surgical resection based on magnetic resonance imaging (MRI) or other imaging evidence alone, a significant fraction will likely additionally require either subdural or depth electrode monitoring for preoperative planning.
A conventional surface strip electrode is diagrammed in FIG. 1: This electrode device (2) has a single row of six electrical contact-points (5) embedded in a silastic matrix (7), each electrode point (5) has an individual wire (6). While six contacts are shown, any number of contacts can and have been implemented. These wires are bundled together (one wire per electrical contact-point) and electrically hardwired to connect to a respective individual contact (9) on a lead/cable. U.S. Pat. No. 6,597,954 B1, FIG. 2, depicts a device 110 having been intracranially implanted and affixed in a patient's cranium 214; the device 110 has a lead connector 220 adapted to receive electrical leads such as that at 222 (which is situated on the outer surface of the cranium 214 under the patient's scalp 112). The six electrode points (5) labeled in FIG. 1 hereof, are conductive for contacting patient tissue (not shown, for simplicity). The bundled leads penetrate out of the skin (for example, see FIG. 11 of U.S. Pat. No. 6,024,702 issued 15 Feb. 2000, where grid electrode 10—such as that in FIG. 5 and FIG. 10—is depicted used as a subdural electrode having been inserted between the brain surface labeled S and the dura labeled D). The several bundled leads are hardwire-connected to a recording machine/unit typically located some distance away from the patient. While invasive electroencephalogram (EEG) using conventional electrodes and associated monitoring units is a commonly used technique for surgical planning, the equipment currently available is cumbersome and monitoring requires expensive in-hospital stays.
To determine if a particular individual with uncontrolled epilepsy is a surgical candidate, two fundamental areas of cerebral cortex must be distinguished, the seizure focus (or foci) and any adjacent eloquent cortex. The seizure focus is that area of cortex where seizures originate(s) and is often abnormal. Surgical resections of a patient's brain are planned and carried out by a surgeon so as to not lead to worsening of neurologic function. Eloquent cortex areas are those areas of brain tissue that control ‘critical functions’ whereby surgical resection of the area would leave a patient impaired. These areas include, but are not limited to, Broca's and Werneke's area that control speech and the motor and sensory strips located in the pre-central and post-central gyri, respectively. While these areas are known anatomically, there is a significant amount of variability between individuals and these functional areas may have been remapped to other anatomical areas due to years of seizure activity. Therefore it is extremely important to have diagnosis tools that aid in accurately identifying those sections of the brain that ought to be removed, if at all.
Multiple techniques have evolved for the localization of the seizure focus and associated eloquent cortex including well-known imaging techniques employing PET and MRI scanners and the use of both invasive and scalp EEG recordings (EEG signals measured represent aggregate neuronal activity potentials detectable via electrodes applied to a patient's scalp or deeper from within). While imaging techniques have the advantage of being non-invasive, not all seizure foci can be determined even with the best available technology. And while useful under certain circumstance, scalp EEG data is not as effective or consistent at lateralizing even the most common surgically treated epilepsy of the temporal lobe. In cases where the seizure focus cannot be determined through imaging, most authorities now recommend invasive EEG monitoring usually taking place in an inpatient video EEG monitoring unit. For seizures related to errors in brain development, invasive EEG is almost always required due to the unpredictability of the seizure focus and eloquent cortex.
The invention described herein is a much improved invasive EEG monitoring system (ActiveInvasive EEG) allowing increased convenience—whether for shorter, outpatient monitoring or prolonged monitoring over an extended period—more accurate data, as well as offering a wider range of applications for invasively monitoring of brain activity and treating neurological disorders (such as epilepsy), for the neurosurgeon, neurologist, associated highly trained medical technicians, and human or veterinary patients. In connection with surgical/preoperative planning done by neurosurgeons and neurologists, the implantable ActiveInvasive EEG device with its design focused at collecting and converting analog signals originating from within the patient's brain nearer to the site of collection, provides the ability for long-term recording and surgical planning, as well as a providing a source of electrical stimulation in treatment of seizures. The implantable ActiveInvasive EEG device, thus, gives neurosurgeons and neurologists another powerful tool for use in surgical planning, treatment, as well as in designing flexible strategies for outpatient monitoring that employs this new EEG device.